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Thread: Venting drainage system in cottage

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    Default Venting drainage system in cottage

    Our family cottage had to be moved back from the lake bluff due to erosion several years back and they moved it over the septic tank. My Grandfather took care of refitting the drainage system after the move. There is one large (4"?) PVC drain from the toilet a branch that comes in from the kitchen sink and one that comes from bathroom sink. The large soil pipe goes directly into the septic tank. All of this is open under the cottage in a crawl space. I don't see any vent and I do notice odors under the cottage, low toilet bowl water and gurgling in my kitchen sink vent after flushing. I'm assuming this is a venting problem. We just got a new well and have been enjoying being able to flush the toilet on a regular basis, wash dishes, shave etc. (the simple things of life). So I'm assuming the increased water flow and usage has kicked up the odor and the problem.
    I've read about vents that can be hooked directely to the waste pipe with a one way valve rather than go to a stack up through the roof, can you vent an entire system this way? Where would the "sewer" gas go, doesn't that need a way out into the atmosphere? Also, Could I just tap into the one big line as it enters the septic with 1 1/2 PVC and go out through the foundation up along the chimney and vent up the roof as is normally done, or am I simplifying this too much?

  2. #2
    In the Trades Gary Swart's Avatar
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    I believe you have some very serious problems here. The house should not be over the septic tank in the first place. Do you have traps on the drains? The air admittance vents, aka Studor, can not be the only drain in a system. There must be at least one vent to the outside. Most plumber shy away from them anyway because they are mechanical devices that can/will fail. I would strongly recommend you contact a licensed plumber to assess your problems. Do not call Grandpa.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by lardlad
    ... one large (4"?) PVC drain from the toilet a branch that comes in from the kitchen sink and one that comes from bathroom sink. The large soil pipe goes directly into the septic tank. All of this is open under the cottage in a crawl space.
    What do you mean by "all of this is open"? Can you see into the septic tank? If so, that definitely needs to be sealed.

    Quote Originally Posted by lardlad
    I don't see any vent ...
    That is believable, and you are going to have to do something about that:

    Quote Originally Posted by lardlad
    ... odors under the cottage, low toilet bowl water and gurgling in my kitchen sink vent after flushing. I'm assuming this is a venting problem.
    Yes, very possibly.

    Quote Originally Posted by lardlad
    I'm assuming the increased water flow and usage has kicked up the odor and the problem.
    You are possibly overloading the septic system, and that would be an additional problem.

    Quote Originally Posted by lardlad
    I've read about vents that can be hooked directely to the waste pipe with a one way valve rather than go to a stack up through the roof, can you vent an entire system this way?
    I am not a real plumber, but I would still say "No." That kind of vent is sometimes used near the trap of a single fixture, but only to protect that particular trap from siphoning.

    Quote Originally Posted by lardlad
    Where would the "sewer" gas go, doesn't that need a way out into the atmosphere?
    Yes ... when you flush, the displaced air in the system must go somewhere.

    Quote Originally Posted by lardlad
    Could I just tap into the one big line as it enters the septic with 1 1/2 PVC and go out through the foundation up along the chimney and vent up the roof as is normally done, or am I simplifying this too much?
    Your overall theory is fine there, but that vent should be at least 2" or even bigger if exposed to freezing weather ... and like Gary said, you really should have a plumber come take a good look. For the price of an estimate or even a service call, s/he should be able and willing to tell you exactly what is going on, what is needed and to alert you to any applicable codes, restrictions or other requirements.
    Last edited by leejosepho; 07-01-2007 at 06:49 PM.

  4. #4

    Default venting

    I have two "Schimpke tanks" in tandem, basically two 4 x 4 concrete tanks with a heavy circular concrete lid. Only the lids are visible. They shouldn't be under the cottage, correct, but they are so I'm stuck with it. Grandpa has long left this mortal coil so it's up to me to figure a way out of the mess. The draings all have traps but no vents anywhere.I think I'll try to do a 2" vent off the main and take it out the back up above the roof line. Can't be any worse than it is now. I'm afraid if I have a plumber out he'll tell me I'm breaking all sorts of codes and won't want to touch a thing. I'll give one a call though and see what they say.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Default vents

    If the traps do not have individual vents, then a vent off the main line will do absolutely nothing to prevent them from siphoning.

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    Licensed Grump GrumpyPlumber's Avatar
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    Quote Originally Posted by hj
    If the traps do not have individual vents, then a vent off the main line will do absolutely nothing to prevent them from siphoning.

    True, consider mechanical venting the individual traps... beats the alternative.
    "The biggest regrets we have in life are the chances we never took."

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by lardlad
    ... odors under the cottage, low toilet bowl water and gurgling in my kitchen sink vent after flushing.
    The low toilet bowl water after flushing *could* be a siphon problem, but the odors under the cottage and the gurgling in the kitchen after a toilet flush are most likely caused by the main line and tank not being vented and leaving the displaced air in the system nowhere to go, correct? And if so, then the toilet bowl is *not* being siphoned since the water has to push its way into the line and tank (thereby causing the gurgling in the kitchen).

    So yes, codes say the fixtures should be vented, but individual fixture-trap vents will not take care of the objectionable symptoms actually being described.
    Last edited by leejosepho; 07-02-2007 at 07:04 PM.

  8. #8
    Licensed Grump GrumpyPlumber's Avatar
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    Quote Originally Posted by leejosepho
    The low toilet bowl water after flushing *could* be a siphon problem, but the odors under the cottage and the gurgling in the kitchen after a toilet flush are most likely caused by the main line and tank not being vented and leaving the displaced air in the system nowhere to go, correct? And if so, then the toilet bowl is *not* being siphoned since the water has to push its way into the line and tank (thereby causing the gurgling in the kitchen).

    So yes, codes say the fixtures should be vented, but individual fixture-trap vents will not take care of the objectionable symptoms actually being described.
    Putting a vent on the kitchen sink trap will stop it from gurgling when the toilet is flushed.
    I've seen it work...though I am NOT a fan of mechanical venting, they do have a tendancy to fail IF they are the spring type...Studor vents are more reliable.
    This guy has the alternative of either ripping open walls, or finding closets to run vents through.
    If his local code allows it, I'd suggest it.
    "The biggest regrets we have in life are the chances we never took."

  9. #9
    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by GrumpyPlumber
    Putting a vent on the kitchen sink trap will stop it from gurgling when the toilet is flushed.
    Yes, I was wrong: an open vent line there (or at any fixture) would take care of air trying to escape from a system that is otherwise closed, as well as to protect the trap from any possible siphoning (which does not seem to be a problem here).

    Quote Originally Posted by GrumpyPlumber
    ...though I am NOT a fan of mechanical venting, they do have a tendancy to fail IF they are the spring type...Studor vents are more reliable.
    That kind of vent would *not* relieve the pressure-gurgling being experienced.

    Quote Originally Posted by GrumpyPlumber
    This guy has the alternative of either ripping open walls, or finding closets to run vents through.
    As an alternative to what he has planned, yes, he could do that if he ultimately discovers he also has a siphoning problem.

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